Hydrochlorothiazide Increases Efferent Glomerular Arteriolar Resistance in Spontaneously Hypertensive Rats

Impact of sex and pathophysiology on optimal drug choice in hypertensive rats: quantitative insights for precision medicine

Less than half of all hypertensive patients receiving treatment are successful in normalizing their blood pressure. Despite the complexity and heterogeneity of hypertension, the current antihypertensive guidelines are not tailored to the individual patient. As a step toward individualized treatment, we develop a quantitative systems pharmacology model of blood pressure regulation in the spontaneously hypertensive rat (SHR) and generate sex-specific virtual populations of SHRs to account for the heterogeneity between the sexes and within the pathophysiology of hypertension. We then used the mechanistic model integrated with machine learning tools to study how variability in these mechanisms leads to differential responses in rodents to the four primary classes of antihypertensive drugs. We found that both the sex and the pathophysiological profile of the individual play a major role in the response to hypertensive treatments. These results provide insight into potential areas to apply precision medicine in human primary hypertension.

Renal T cell infiltration occurs despite attenuation of development of hypertension with hydralazine in Envigo's female Dahl rat maintained on a low-Na+ diet

Many studies have suggested that renal T cell infiltration contributes to the pathogenesis of salt-sensitive hypertension. To investigate this mechanism further, we determined T cell profiles in the kidney and lymphoid tissues as a function of blood pressure in the female Envigo Dahl salt-sensitive (SS) rat maintained on low-Na+ (LS) diet. Mean arterial pressure and heart rate were measured by telemetry in SS rats from 1 mo old (juvenile) to 4 mo old. Normotensive salt-resistant (SR) rats were included as controls. Frequencies of T helper (CD4+) cells were greater in the kidney, lymph nodes, and spleen in 4-mo-old hypertensive SS rats compared with normotensive SR animals and SS juvenile rats, suggesting that renal T cell infiltration contributes to hypertension in the SS rat on a LS diet. At 1.5 mo, half of the SS rats were treated with vehicle (Veh), and the rest received hydralazine (HDZ; 25 mg·kg-1·day-1) for 11 wk. HDZ impeded the development of hypertension compared with Veh-treated control rats [mean arterial pressure: 157 ± 4 mmHg in the Veh-treated group (n = 6) vs. 133 ± 3 mmHg in the HDZ-treated group (n = 7), P < 0.001] without impacting T helper cell frequencies in the tissues, suggesting that HDZ can overcome mechanisms of hypertension driven by renal T cell infiltration under the LS diet. Renal frequencies of CD4+CD25+ and CD4+CD25+FoxP3+ regulatory T cells were significantly higher in 4-mo-old hypertensive rats compared with normotensive SR rats and SS juvenile rats, suggesting that these T cell subpopulations play a compensatory role in the development of hypertension. Greater understanding of these T cell populations could lead to new therapeutic targets for treating inflammatory diseases associated with hypertension.

Angiotensin receptor blockade has protective effects on the poststenotic porcine kidney

Angiotensin converting enzyme inhibitors (ACEI)/ angiotensin-II receptor blockers (ARBs) may induce an acute decrease of glomerular filtration rate (GFR) in the stenotic kidney in renal artery stenosis, but most patients tolerate these drugs well. We hypothesized that ACEI/ARBs stabilize stenotic kidney function during prolonged treatment by conferring protective effects. We tested this in control domestic pigs and pigs with renal artery stenosis untreated or treated with valsartan, or triple therapy (7 pigs in each group) for 4 weeks starting 6 weeks after stenosis induction. Renal function, oxygenation, tubular function, and microcirculation were assessed by multi-detector computed tomography (CT), blood-oxygen-level-dependent magnetic-resonance imaging, and micro-CT. Valsartan and triple therapy decreased blood pressure similarly, however, valsartan did not change the GFR of the stenotic kidney compared to renal artery stenosis and was similar to triple therapy. Both valsartan and triple therapy stimulated microvascular density, and improved tubular function. Valsartan also caused a greater increase of angiogenic factors and a decrease in oxidative stress, which were related to higher cortical perfusion and tubular response than triple therapy. Thus, valsartan did not decrease stenotic kidney GFR, but improved cortical perfusion and microcirculation. These beneficial effects may partly offset the hemodynamic GFR reduction in renal artery stenosis and preserve kidney function.

Chlorthalidone Decreases Platelet Aggregation and Vascular Permeability and Promotes Angiogenesis

Variations in diuretic-mediated inhibition of carbonic anhydrase-dependent chloride transport in platelets and vascular smooth muscle could account for the contrasting efficacy of the thiazide and thiazide-like diuretics in reducing cardiovascular morbidity in patients with hypertension. We assessed platelet carbonic anhydrase activity and catecholamine-induced platelet aggregation in the presence of a thiazide and a “thiazide-like” inhibitor of the sodium-chloride cotransporter. Individual variation in platelet carbonic anhydrase activity correlated with contrasting sensitivity to epinephrine-mediated platelet aggregation. Both chlorthalidone, which potently inhibits platelet carbonic anhydrase, and bendroflumethiazide, which has much less effect on this enzyme, increased the amount of epinephrine needed to induce platelet aggregation when compared with the absence of a diuretic. However, chlorthalidone was significantly more effective than bendroflumethiazide in reducing epinephrine-mediated platelet aggregation. Chlorthalidone also induced marked changes in the number of gene transcripts for two proteins that mediate angiogenesis and vascular permeability, vascular endothelial growth factor C and transforming growth factor-β3; chlorthalidone and bendroflumethiazide had contrasting effects on the expression of vascular endothelial growth factor C. Chlorthalidone and bendroflumethiazide reduced vascular permeability to albumin, but only chlorthalidone increased angiogenesis. Thiazides and thiazide-like diuretics can comparably reduce blood pressure, but the drugs in this class are not all alike. It can be suggested from our findings that thiazide and thiazide-like diuretics vary in their pleiotropic effects on platelets and in the vasculature, and these differences could explain the contrasting ability of these drugs to reduce cardiovascular morbidity despite comparable reduction in blood pressure.

Thiazide-induced subtle renal injury not observed in states of equivalent hypokalemia

Hydrochlorothiazide (HCTZ) is used to manage hypertension and heart failure; however, its side effects include mild hypokalemia, metabolic abnormalities, and volume depletion, which might have deleterious effects on renal and endothelial function. We studied whether HCTZ cause renal injury and/or altered vasoreactivity and if these changes are hypokalemia-dependent. Rats were given a normal diet or a diet moderately low in potassium K+ with or without HCTZ. Animals fed either a low K+ diet alone or HCTZ developed mild hypokalemia. There was no significant difference in systolic blood pressure in the different treatment groups. All three groups with hypokalemia had mild proteinuria; low K(+)-HCTZ rats had reduced creatinine clearance. HCTZ-treated rats displayed hypomagnesemia, hypertriglyceridemia, hyperglycemia, insulin resistance, and hyperaldosteronism. No renal injury was observed in the groups without HCTZ; however, increased kidney weight, glomerular ischemia, medullary injury, and cortical oxidative stress were seen with HCTZ treatment. Endothelium-dependent vasorelaxation was reduced in all hypokalemic groups and correlated with reduced serum K+, serum, and urine nitric oxide. Our results show that HCTZ is associated with greater renal injury for the same degree of hypokalemia as the low K+ diet, suggesting that factors such as chronic ischemia and hyperaldosteronism due to volume depletion may be responsible agents. We also found impaired endothelium-dependent vasorelaxation was linked to mild hypokalemia.

Is population-wide diuretic use directly associated with the incidence of end-stage renal disease in the United States?

In the quest for "evidence-based" medicine, an accepted hierarchy of evidence has been proposed. This hierarchy places in vitro studies and animal data at the base, and puts systematic reviews, meta-analyses, and randomized controlled trials at the pinnacle. However, when clinical medicine faces questions that have not yet been studied by the "gold standard" methods, how is one to proceed? Often, the best evidence at hand falls short of randomized controlled trials and meta-analyses. Using this framework, a review of the evidence supporting the hypothesis that population-wide diuretic use is directly associated with end-stage renal disease in the United States is presented. Publications pertaining to diuretic use in recent clinical trials are also discussed.

Superiority of combination of thiazide with angiotensin-converting enzyme inhibitor or AT1-receptor blocker over thiazide alone on renoprotection inl-NAME/SHR

The renal and glomerular dynamic effects of combining thiazide and angiotensin antagonists have not been reported. The present study was designed to examine the effects of hydrochlorothiazide (HCTZ) alone or in combination with an angiotensin-converting enzyme inhibitor or ANG II type 1-receptor blocker on renal hemodynamics, glomerular dynamics, renal function, and renal histopathology in the Nω-nitro-l-arginine methyl ester-treated spontaneously hypertensive rat (l-NAME/SHR) model. HCTZ (80 mg·kg−1·day−1) alone or in combination with enalapril (30 mg·kg−1·day−1) or losartan (30 mg·kg−1·day−1) or enalapril (15 mg·kg−1·day−1) plus losartan (15 mg·kg−1·day−1) was administered to l-NAME/SHR (5.0 ± 0.10 mg·kg−1·day−1) for 3 wk. Mean arterial pressure, total peripheral resistance, renal plasma flow, glomerular filtration rate, glomerular hydrostatic pressure, afferent and efferent glomerular arteriolar resistances, single nephron plasma flow, single nephron glomerular filtration rate, serum creatinine concentration, 24-h urinary protein excretion, and glomerular and arteriolar injury scores were determined. HCTZ reduced mean arterial pressure, total peripheral resistance, glomerular hydrostatic pressure, and afferent and efferent glomerular arteriolar resistances ( P < 0.05, at least) but slightly increased renal plasma flow and single nephron plasma flow associated with reduced serum creatinine concentration, urinary protein excretion, and arteriolar injury score compared with l-NAME/SHR control. However, the combination of enalapril and/or losartan with HCTZ markedly improved each of these functions. These results demonstrated minor benefits of HCTZ monotherapy and a marked superiority of its combination with enalapril and/or losartan over HCTZ monotherapy on renoprotection in l-NAME/SHR, thereby providing strong evidence of their clinical benefits for hypertensive patients with renal functional impairment.

Hypertension and atherosclerosis: clinical implications from the ALLHAT Trial

By failing to recognize the heterogeneity of hypertension, the authors of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial (ALLHAT) study used a faulty premise to conduct a poorly designed clinical trial. By failing to control blood pressures equally across study drug groups, ALLHAT cannot be considered to be a definitive comparative trial. Being neither a monotherapy trial nor a trial that initiated therapy for blood pressure control, ALLHAT provided no data to recommend first-line therapy for hypertension, making the conclusions invalid. Thiazide-type diuretics increase angiotensin II and consequently promote atherosclerosis and arteriolarsclerosis. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers retard atherosclerosis and are nephroprotective. Multiple randomized controlled trials show beneficial clinical outcomes, including cardioprotection and nephroprotection, with the use of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. These agents, and not thiazide-type diuretics, should be used as first-line agents to retard the process of atherosclerosis and its clinical outcomes in the setting of arterial hypertension.

Arthus C. Corcoran Memorial Lecture. Influence of nitric oxide and angiotensin II on renal involvement in hypertension

Remarkable advances have been made with prolonged antihypertensive therapy in reversing cardiovascular morbidity and mortality. Deaths from stroke have been reduced by 70% and from coronary heart disease by 35%. In contrast, endstage renal disease resulting from hypertension continues to increase. The explanations for this seeming paradox remain unresolved even though experimental models have demonstrated that certain antihypertensive agents may have beneficial renal and intrarenal hemodynamic effects; but reversal of the intrarenal pathological lesions have not been shown to improve. This discussion summarizes recent studies from our laboratory in aged (73- and 85-week-old) spontaneously hypertensive rats (SHR) with naturally occurring end-stage renal disease and in a model of aged SHR employing nitric oxide inhibition in younger, adult (20-week-old) SHR. Our findings demonstrated that the systemic and whole renal hemodynamics, intrarenal glomerular dynamics, proteinuria, and renal pathological lesions can be prevented or reversed with angiotensin-converting enzyme inhibition therapy but not with hydrochlorothiazide (at similar levels of arterial pressure reduction). The implications and possible mechanisms involved in the development of both naturally occurring and nitric oxide-exacerbated SHR are multifactorial, involving the endothelial nitric oxide system and its interaction with angiotensin II (and possibly bradykinin) among other factors. Moreover, these pathophysiological cellular mechanisms may be shared by the aging process as well as in naturally occurring spontaneous hypertension in the rat and, perhaps, in humans with essential hypertension. Thus, antihypertensive therapy seems to be specific in its ability to prevent and even reverse the pathophysiological derangements of renal involvement in hypertension. Thus, prevention and reversal of end-stage renal disease do not seem to require greater reduction of arterial pressure than with other target-organ involvement. However, they do require specific inhibition of the arteriolar and glomerular lesions produced by the disease.